编程珠玑的一道令我surprise的题目，竟然和Google的笔试题一样。

其实题目很简单，就是计算一个整数数组中，连续的最大子数组。



一开始想到肯定是个O(n*n)的算法：maxSectionGood
后来使用递归O(n*log(n))：maxSectionExcellent
最经典的是最后一个算法，提升到了O(n)：maxSectionPrefect

Google 笔试题：

input: an array of int which represent a binary number the bit is 1

output: the count of 1 triple of the number

input: an array of int

output: the max sum of continual element of the array of input

#include <iostream>
#include <string>
#include <vector>
#include <stdlib.h>
using namespace std;
int maxThree(int a,int b, int c)
{
	if ((a>=b)&&(a>=c))
		return 0;
	if ((b>=1)&&(b>=c))
		return 1;
	if ((c>=b)&&(c>=a))
		return 2;
}
int maxSectionGood(vector<int> inArray)
{
	int max = inArray[0];
	for(unsigned int i=0;i<inArray.size();i++)
	{
		int sum = 0;
		for(unsigned int j=i;j<inArray.size();j++)
		{
			sum = sum + inArray[j];
			if (sum>max)
			{
				max = sum;
			}
		}
	}
	return max;
}
int maxSectionExcellent(vector<int> inArray, int& startIndex)
{
	if (inArray.size()>1)
	{
		int t = inArray[inArray.size()-1];
		inArray.pop_back();
		int fromIndex = 0;
		int maxsofar = maxSectionEnhanced(inArray,fromIndex);
		int sum = t;
		int tempmax = t;
		for (int i=inArray.size()-1; i>=fromIndex; i--)
		{
			sum=sum+inArray[i];
			if (sum>tempmax)
			{
				tempmax = sum;
				startIndex = i;
			}
		}
		int maxThreeR = maxThree(t,sum,maxsofar);
		if (maxThreeR==0)
		{
			startIndex = inArray.size();
			return t;
		}
		if (maxThreeR==1)
		{
			startIndex = fromIndex;
			return sum;
		}
		if (maxThreeR==2)
		{
			startIndex = fromIndex;
			return maxsofar;
		}
	}else
	{
		startIndex = 0;
		return inArray[0];
	}
}
int max(int a,int b)
{
	if (a>b)
		return a;
	else
		return b;
}
int maxSectionPrefect(vector<int> inArray)
{
	int maxsofar = 0;
	int masendinghere=0;
	for (int i=0;i<inArray.size();i++){
		masendinghere = max(masendinghere+inArray[i],0);
		maxsofar = max(maxsofar,masendinghere);
		cout<<"masendinghere:"<<masendinghere<<" maxsofar:"<<maxsofar<<endl;
	}
	if( masendinghere>maxsofar)
		return masendinghere;
	else
		return maxsofar;
}
/*
int main() {
	vector<int> t;
	t.push_back(31);
	t.push_back(-41);
	t.push_back(59);
	t.push_back(26);
	t.push_back(-53);
	t.push_back(58);
	t.push_back(97);
	t.push_back(-93);
	t.push_back(-23);
	t.push_back(84);
	int start=0;
	int result = maxSectionPrefect(t);
	//int result = maxSectionExcellent(t,start);
	//int result = maxSectionGood(t);
	cout << "Result: " << result << endl; // prints !!!Hello World!!!
	return 0;
};
*/